Although horizontal or lateral wells are well known in the art, horizontal well drilling and production have not been significant aspects of the industry until recently. Even though horizontal drilling is much more expensive than conventional vertical drilling, well production can be increased greatly when it is used appropriately. In general, productivity must be more or less tripled to justify the increased cost of a horizontal well. In the case of naturally fractured reservoirs and thin reservoirs, production can be increased tenfold or more, so that relative cost is not a deterrent to horizontal drilling. In many situations, the horizontal well is drilled as a lateral from a main vertical wellbore. This is an especially common practice on offshore platforms, where the increased production of a lateral well, or multilateral wells, allows a field to be developed with fewer platforms.
As a result of the increased usage of lateral wells, lateral and multi-lateral well completion and subsequent production and servicing have become an important concern. Well service operations require the ability to selectively reenter, or access subterranean wellbores to perform completion or well servicing work. It is desirable and cost effective for the system to be such that the selected wellbore can be accessed with a coiled tubing or wireline rig, so that the a full drilling rig is not required. Furthermore, it is desirable to minimize the number of trips required to access and work a selected lateral wellbore, the more cost effective a lateral well completion system will be. For example, U.S. Pat. No. 2,211,803, issued Aug. 20, 1940 to W. A. Warburton describes a selective access system, which requires multiple trips to install and remove a sleeve to selectively block access to a bore.
Only recently has the ability to access one or more lateral wellbores from a main wellbore become important within the exploration industry and present prior art devices do not address this need. Prior art multilateral wellbore completion systems presently employ sliding sleeves to open and close small ports specifically designed for circulation and production control purposes but not for providing tool access into a lateral wellbore. Consequently, these systems are ineffective for the more recent problems of completion, production and work-over of a wellbore with one or more lateral wellbores.
Therefore, the first object of the present invention is to provide an apparatus and method for main and multilateral wellbore completion and production with access capability for tools into any selected wellbore. A second object is that this system has the ability to provide connectivity and isolation as described above, so that structurally sound, hydraulically sealed junctures can be made between main and lateral wellbores. A third object is to provide tool access to such a system by coiled tubing or wireline rigs, so that the services of a full drilling rig will not be required. Yet another object is to minimize the number of trips required to access and work a selected lateral wellbore.